>White text scatters over the iris on a dark background, so it’s harder to read the copy. I’ve even read it in UX articles.
That doesn't make sense. Why does light from white text scatter, but not light from white background?
That doesn't make sense. Why does light from white text scatter, but not light from white background?
The effect you're describing is correct, but the mechanism isn't. Aperture (pupil) size directly affects how focused the image is. The smaller the aperture, the sharper the image is. As an extreme example, if your aperture is a single point (a pinhole camera), the image can be focused without a lens.
https://en.wikipedia.org/wiki/Aperture#Maximum_and_minimum_a...
>I couldn’t find a scientific source on this, but a couple articles called it the “Halation effect”.
Articles describing this seems to say it's caused by the film medium, rather than being an optical effect.
Yeah, I noticed that. Searching the term directly gave me results related to film, but when I used other terms describing the effect they mentioned it in a different context. Makes me wonder if someone is just confused.
Diffraction limits the sharpness, though. https://en.wikipedia.org/wiki/Diffraction-limited_system. Pesky wave nature of light in action.
> Articles describing this seems to say it's caused by the film medium, rather than being an optical effect.
Halation in film is caused by reflection from the back of the film. Most of them have an anti-halation layer to reduce this effect. I don't see any reason why one's eye wouldn't also be vulnerable to this effect (and probably has some biological mechanism to prevent light from being reflected out of the eye. Cats sure don't have this, though.)
Specifically, bright light results in a small pupil which allows for better focus. And low light results in a large pupil which reduces focus.